1. Field of the Invention
This invention relates to a method of performing thermal multicolor printing on a paper.
2. Prior Art
FIG. 1 is a side elevational view of one conventional thermal transfer type multicolor printer. In FIG. 1, shown at 1 is a print paper with feed holes which engage with sprocket pins 2a of a pair of paper feed sprocket wheels 2 connected by a shaft 2b. The paper 1 fed by the sprocket wheels 2 is guided by a pair of guide rollers 3 mounted on opposite ends of a shaft 3a, wrapped around a platen roller 4 by about 240.degree., and then extends upward of a paper cutter 5 having a sharp cutting edge. The platen roller 4 is formed at opposite peripheral edge portions thereof with sprocket pins 4a, and the feed holes of the paper 1 also engage with these sprocket pins 4a. The platen roller 4 is operatively connected to an output shaft of a drive motor 6 such as a stepping motor, and is also connected to the sprocket wheels 2 through a transmission mechanism such as a timing belt, so that, when driven, the platen roller 4 rotates with the sprocket wheels at the same peripheral speed. Shown at 7 is an ink ribbon which is fed from a supply reel 8, guided by the shaft 3a, wrapped around the platen roller 4 such that the paper 1 is disposed between this ink ribbon 7 and the peripheral surface of the platen roller 4, guided by guide rollers 9 and 10, and then taken up by a take-up reel 11. This take-up reel 11 is driven by a motor 12 such as a stepping motor.
As shown in FIG. 2, the ink ribbon 7 comprises a base 14 made of a condenser paper, a polyester film or the like which has a width less than the distance between the pair of sprocket wheels 2. A plurality of ink zones 15a, 15b, 15c, 15a, . . . of the same length l are formed on the base 14 at a predetermined pitch P by applying to one surface thereof wellknown heat-dissolving yellow, magenta and cyan inks, each color ink appearing every three ink zones 15. Provided in each blank portion 16 of the base 14 disposed between adjoining ink zones 15 and 15 is a sensor mark 17a, 17b or 17c for being detected by a photosensor device 18 (FIG. 1), disposed between the rollers 9 and 10, to determine the color of the ink zone which comes immediately after the detected mark. Each of the marks 17 may be a through hole or a metal piece.
The conventional printer is also provided with a retractable thermal head 19 having a plurality of heater elements arranged in a row transversely of the paper 1 for thermally printing a row or a line of dots on the paper 1. The head 19 is urged against the platen roller 4 through the ink ribbon 7 and the paper 1 when an actual printing operation is to be performed, and is retracted from the platen roller 4 when the actual printing operation is not performed, i.g., when the paper 1 is fed in the reverse direction.
The operation of this conventional multi-color printer will now be described with reference to a flow chart shown in FIG. 3.
At first, the paper 1 is set to the printer so that the leading edge of the first page thereof, on which a color image is to be printed, is in agreement with the thermal print head 19. Then, the printer is brought into a printing operation by a depression of a start button (not shown) by the operator, whereupon the motor 12 is driven so that the leading edge of the yellow ink zone 15a is automatically comes into agreement with the the head 19. Thus, the yellow ink zone 15a is registered with the page of the paper 1. Thereafter, the heating elements of the head 19 are activated in accordance with data representative of yellow component dots of the multicolor image, and the motors 6 and 12 are driven to feed the paper 1 and the ribbon 7 in steps in the forward direction in unison with each other to thereby print the yellow component dots on the page of the paper 1 (step SP1). When the printing operation of the yellow component dots is completed, the paper 1 and the ink ribbon 7 are in adhered relation to each other due to the dissolved ink at that portions disposed between the thermal head 19 and the guide roller 9. To separate the paper 1 from the ink ribbon 7, the paper 1 and the ribbon 7 are further advanced by a predetermined distance (step SP2). When this further advance is completed, the leading edge of the magenta ink zone 15b is in agreement with the head 19. Then, the motor 6 is driven so as to rotate in the reverse direction to thereby move the paper 1 backwardly to the initial position where the leading edge of the page thereof is in registry with the head 19. Then, the printing of the magenta component dots of the image is performed in a manner described for the printing of the yellow component dots (step SP3), and after this the separation of the ink ribbon 7 from the paper 1 is effected (step SP4). Then, the paper 1 is again fed backwardly, and subsequently the printing of the cyan component dots of the image is performed (step SP5). The paper 1 is then separated from the ink ribbon 7 (step SP6) by further feeding them in the forward direction, whereupon the multicolor printing of the image on the page is completed. Then, the paper 1 is further fed in the forward direction so that the trailing edge of the printed page reaches the cutting edge of the paper cutter 5 to terminate the printing operation (step SP7).
As will be appreciated from the foregoing, it is essential for the multicolor thermal printer to separate the print paper 1 from the ink ribbon 7 by forwardly feeding both of the paper and ink ribbon (steps SP2, SP4 and SP6), and the length of each ink zone is restricted. As a result, when printing over a plurality of consecutive pages is performed, a blank of a predetermined length is left at each boundary between adjoining pages. This is undesirable particularly when the printer is used in place of a pen-type recorder, that is, when it is required to print one lengthy color image over a plurality of pages of a print paper. To enable the printer to print one lengthy color image, the ink ribbon may be modified to have ink zones greater in length. However, such ink ribbon is liable to be subject to wrinkle.